Imprint lithography

ABSTRACT

An imprint lithography apparatus is disclosed that includes a support structure configured to hold an imprint template. The apparatus further includes an actuator located between the support structure and a side of the imprint template, when the imprint template is held by the support structure, configured to apply a force to the imprint template and a force sensor between the support structure and a side of the imprint template, when the imprint template is held by the support structure.

This application is a continuation of U.S. patent application Ser. No.14/076,793, filed Nov. 11, 2013, now allowed, which is a continuation ofU.S. patent application Ser. No. 12/285,698, filed Oct. 10, 2008, nowU.S. Pat. No. 8,579,625, which claims the benefit of priority from U.S.provisional patent application Ser. No. 60/960,727, filed on Oct. 11,2007, the entire content of each of the foregoing applications isincorporated herein by reference.

FIELD

The present invention relates to imprint lithography.

BACKGROUND

In lithography, there is an ongoing desire to reduce the size offeatures in a lithographic pattern to increase the density of featureson a given substrate area. In photolithography, the push for smallerfeatures has resulted in the development of technologies such asimmersion lithography and extreme ultraviolet (EUV) lithography, whichare however rather costly.

A potentially less costly road to smaller features that has gainedincreasing interest is so-called imprint lithography, which generallyinvolves the use of a template to transfer a pattern onto a substrate.An advantage of imprint lithography is that the resolution of thefeatures is not limited by, e.g., the wavelength of a radiation sourceor the numerical aperture of a projection system as in photolithography,but mainly just by the pattern density on the template (also referred toas a stamp). There are three main approaches to imprint lithography,examples of which are schematically depicted in FIGS. 1a to 1 c.

FIG. 1a shows an example of a type of imprint lithography that is oftenreferred to as micro-contact printing. Micro-contact printing involvestransferring a layer of molecules 11 (typically an ink such as a thiol)from a template 10 (e.g. a polydimethylsiloxane template) onto a resistlayer 13 which is supported by a substrate 12 and planarization andtransfer layer 12′. The template 10 has a pattern of features on itssurface, the molecular layer being disposed upon the features. When thetemplate comes into contact with the resist layer, the layer ofmolecules 11 are transferred onto the resist. After the templatedisengages from contact with the resist layer, the resist is etched suchthat the areas of the resist not covered by the transferred molecularlayer are etched down to the substrate. For more information onmicro-contact printing, see e.g. U.S. Pat. No. 6,180,239.

FIG. 1b shows an example of so-called hot imprint lithography (or hotembossing). In a typical hot imprint process, a template 14 is imprintedinto a thermosetting or a thermoplastic polymer resin 15 (more generallyan imprintable medium), which has been cast on the surface of asubstrate 12. The resin may, for instance, be spin coated and baked ontothe substrate surface or, as in the example illustrated, onto aplanarization and transfer layer 12′. When a thermosetting polymer resinis used, the resin is heated to a temperature such that, upon contactwith the template, the resin is sufficiently flowable to flow into thepattern features defined on the template. The temperature of the resinis then increased to thermally cure (crosslink) the resin so that itsolidifies and irreversibly adopts the desired pattern. The template maythen disengage and the patterned resin cooled. In hot imprintlithography employing a layer of thermoplastic polymer resin, thethermoplastic resin is heated so that it is in a freely flowable stateimmediately prior to imprinting with the template. It may be necessaryto heat a thermoplastic resin to a temperature considerably above theglass transition temperature of the resin. The template engages theflowable resin, which cooled to below its glass transition temperaturewith the template in place to harden the pattern. Thereafter, thetemplate disengages. The pattern will consist of the features in relieffrom a residual layer of the resin, which residual layer may then beremoved by an appropriate etch process to leave only the patternfeatures. Examples of thermoplastic polymer resins used in hot imprintlithography processes are poly (methyl methacrylate), polystyrene, poly(benzyl methacrylate) or poly (cyclohexyl methacrylate). For moreinformation on hot imprint, see e.g. U.S. Pat. Nos. 4,731,155 and5,772,905.

FIG. 1c shows an example of ultraviolet (UV) imprint lithography, whichinvolves the use of a transparent template and a UV-curable liquid as animprintable medium (the term “UV” is used here for convenience butshould be interpreted as including any suitable actinic radiation forcuring the resist). An UV curable liquid is often less viscous than athermosetting and thermoplastic resin used in hot imprint lithographyand consequently may move much faster to fill template pattern features.A quartz template 16 is applied to a UV-curable resin 17 in a similarmanner to the process of FIG. 1b . However, instead of using heat ortemperature cycling as in hot imprint, the pattern is frozen by curingthe resin with UV radiation that is applied through the quartz templateonto the resin. After the template disengages, the pattern will consistof the features in relief from a residual layer of the resin, whichresidual layer may then be removed by an appropriate etch process toleave only the pattern features. A particular manner of patterning asubstrate through UV imprint lithography is so-called step and flashimprint lithography (SFIL), which may be used to pattern a substrate ina number of subsequent steps in a similar manner to optical steppersconventionally used in IC manufacture. For more information on UVimprint, see e.g. United States published patent application2004-0124566, U.S. Pat. No. 6,334,960, PCT patent applicationpublication no. WO 02/067055, and the article by J. Haisma entitled“Mold-assisted nanolithography: A process for reliable patternreplication”, J. Vac. Sci. Technol. B14(6), November/December 1996.

Combinations of the above imprint techniques are also possible. See,e.g., United States patent application publication no. 2005-0274693,which mentions a combination of heating and UV curing a resist.

SUMMARY

There are possible applications of imprint lithography in which it isdesirable to apply a force to the imprint template, in order to deformthe template to a desired extent. Examples of such applications includemagnification correction (typically demagnification), shape correction,and an imprint technique utilizing a curved flexible imprint template.

Although magnification correction and shape correction may be of benefitin overcoming the effect of temperature, wear and/or manufacturingdefects on imprint template function, a difficulty may arise in ensuringthat a desired amount of force is applied to an imprint template, andthus that a desired amount of deformation is attained. A difficulty inapplying a desired amount of force may occur as a result of uncertaintyregarding the force applied by an actuator to a peripheral edge of theimprint template. Such uncertainty may arise as a result of misalignmentor introduction of a gap during manufacture or fitting of an imprinttemplate, and/or due to distortion of a supporting structure againstwhich the actuator abuts.

Similarly, although the use of a bent template (as outlined above withreference to FIG. 3) provides an advantage over a conventional imprintlithography technique it may, in certain circumstances, be difficult toensure that a desired amount of force is applied to an imprint template,and thus that a desired degree of curvature is attained. A difficulty inapplying a desired amount of force may arise as a result of uncertaintyregarding the force applied by the actuator to a peripheral edge of theimprint template. Such uncertainty may arise as a result of misalignmentor introduction of a gap during manufacture or fitting of an imprinttemplate, and/or due to distortion of a supporting structure againstwhich the actuator abuts.

It is desirable to provide, for example, an imprint lithographyapparatus and method which overcomes or mitigates at least one problemassociated with the art, whether identified herein or elsewhere.

According to an aspect of the present invention, there is provided animprint lithography apparatus comprising a support structure configuredto hold an imprint template; an actuator located between the supportstructure and a side of the imprint template, when the imprint templateis held by the support structure, configured to apply a force to theimprint template; and a force sensor between the support structure and aside of the imprint template, when the imprint template is held by thesupport structure.

According to an aspect of the present invention, there is provided animprint lithography apparatus, comprising: an imprint template supportedby a support structure; an actuator, located between the supportstructure and a side of the imprint template, configured to apply aforce to the imprint template; and a force sensor located between thesupport structure and a side of the imprint template.

According to an aspect of the present invention, there is provided animprint lithography method, comprising: applying a force to a side of animprint template; assessing the force applied to the imprint template bymeans of a force sensor; and determining whether the force applied tothe imprint template is sufficient to achieve a desired deformation ofthe imprint template.

According to an aspect of the present invention, there is provided animprint lithography method comprising: applying a force to a side of animprint template; assessing the force applied to the imprint template bymeans of a force sensor; and determining whether the force applied tothe imprint template is sufficient to achieve a desired curvature of theimprint template.

According to an aspect of the present invention, there is provided animprint lithography apparatus comprising an imprint template supportedby a support structure, an actuator located between the supportstructure and a side of the imprint template configured to apply a forceto the imprint template, wherein the actuator is arranged to apply aforce to a side of the imprint template at a position substantially onthe neutral plane of the imprint template.

According to an aspect of the present invention, there is provided animprint lithography apparatus comprising a support structure configuredto support an imprint template, the support structure comprising anactuator arranged to apply a force to a side of the imprint template ata position substantially on the neutral plane of the imprint template.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1b and 1c schematically show examples of, respectively,micro-contact printing, hot imprint, and UV imprint;

FIGS. 2a and 2b schematically show an imprint lithography processutilizing a magnification correction technique;

FIGS. 3a and 3b schematically show the flow of liquid and gas during animprint process utilizing a bent imprint template;

FIGS. 4a and 4b schematically show an imprint apparatus according to anembodiment of the present invention

FIGS. 5a and 5b schematically show an imprint apparatus according to anembodiment of the present invention;

FIGS. 6a, 6b, and 6c schematically show an imprint apparatus accordingto an embodiment of the present invention;

FIGS. 7a, 7b and 7c schematically show use of the apparatus of FIGS. 6aand 6b in an imprint lithography process utilizing a curved imprinttemplate; and

FIG. 8 shows a detail of an imprint apparatus according to an embodimentof the invention.

DETAILED DESCRIPTION

Magnification correction is a technique in which force is applied to animprint template in order to deform and compress the template, and hencethe pattern carried on the template, to counteract the effect of achange in the size of the template, such as that may occur as a resultof thermal expansion. Shape correction involves the application of forceto a template to counteract a change in the shape of the template andthe pattern carried thereon. Magnification correction and/or shapecorrection may be used in order to ensure correct registration ofsequential lithographic imprints superimposed on the same substrate tomeet overlay requirements. An apparatus or method as disclosed hereinmay be used in a magnification correction technique and/or a shapecorrection technique.

Magnification or shape correction techniques may be used to deform atemplate, as described above, in order to counteract the effect of achange in the size or shape of the substrate on which imprinting is tooccur. Such a change of a substrate may be caused by expansion, or otherstress, of the substrate, or to a difference in size or shape of one ormore elements formed in a preceding lithography step (e.g. a precedingoptical or imprint lithography step).

FIG. 2 shows an imprint lithographic technique utilizing magnificationcorrection to achieve demagnification.

In this technique an imprint template 18 is supported in a supportstructure 21, and one or more actuators 19 are located between thesupport structure 21 and the peripheral side(s) of the imprint template.In FIG. 2a , the imprint template 18 is shown with two features 18 athat are to be imprinted onto corresponding features 20 a on apreviously imprinted substrate 20. Thermal expansion of the template 18is such that, in its normal resting state, features 18 a on the templateare not aligned with features 20 a on the substrate.

In order to achieve correction of the magnification that has taken placeas a result of thermal expansion, the actuator(s) 19 is used to deformthe template 18 to counteract the effect of thermal expansion. Theextent of expansion is assessed, and from this the amount of force to beapplied to the imprint template 18 in order to offset the expansion iscalculated. As shown in FIG. 2b , urging of the actuator(s) 19 againstsupport structure 21 and the peripheral side(s) of the imprint template18 applies force to the template, and causes the imprint template todeform inwardly towards the center of the template. This deformation issufficient to compress the template 18, and thereby allow alignment offeatures 18 a on the imprint template with features 20 a on thesubstrate 20. Once alignment has been achieved imprinting may then takeplace.

In addition or alternatively to counteracting an increase in the size ofan imprint template resulting from, e.g., thermal expansion of thetemplate, a similar correction technique may be used to correct anirregularity in the shape of the template or substrate, or the patternon the template or substrate, that may arise, for example, duringmanufacture or as a result of subsequent wear. In this case, the forcerequired to offset the irregularity in the shape of the template orsubstrate is calculated, and the applicable force is applied to thetemplate by the actuator(s) 19.

The use of a curved flexible imprint template has been suggested as animprovement of existing imprint lithographic techniques. In theabove-mentioned approaches to imprint lithography, especially hotimprint lithography and UV imprint lithography, an imprint liquid issandwiched between a substrate and a template to form a thin continuouslayer over the entire area of the template. When the imprint liquid issandwiched between the substrate and the template, the liquid isexpelled outwardly, so that it ultimately forms a thin continuous layerof liquid. At the same time, gas (e.g., air) present between thetemplate and the substrate is also sandwiched. As the distance betweentemplate and substrate reduces it is more difficult for the imprintliquid and gas to flow outwardly and around features of the template.The closer the template is to the substrate, the more slowly the imprintliquid flows. Thus, since the imprint liquid flows slowly, the timetaken to form a thin continuous layer increases. Similarly, the closerthe template is to the substrate, the longer it takes to expel gas frombetween the imprint template and the substrate. It is also possible thatgas sandwiched between the template and the substrate may becometrapped, forming gas bubbles that may introduce defects into the imprintpattern.

To try to address such a problem (or one or more other problems), it hasbeen suggested to utilize an imprint lithography apparatus and method inwhich force is applied to an imprint template or imprint template holdersuch that the imprint template or imprint template holder bends andforms an outwardly curved surface. This outwardly curved surface is thenused to impart a pattern onto imprint liquid on a substrate.

FIG. 3a shows the use of an imprint template 22 that has been bent bythe application of force to its peripheral edge(s) by one or moreactuators 23. The template is bent such that an outwardly curved surface22 a is formed, and this curved surface is used to imprint a patternonto imprint liquid 24 deposited on the substrate 21. FIG. 3billustrates the bent imprint template 22 coming into contact with theimprint liquid 24.

Because the outwardly curved surface 22 a of the imprint template 22 isused to impart a pattern in the imprint liquid 24 on the substrate 21,the gap between the imprint template 22 and the substrate 21 increasesfrom the center to the edge(s) of the imprint template 22. As a resultthe imprint liquid 24 and gas 26 may flow more readily away from thecenter of the imprint template 22. As a result of the improved flow ofimprint liquid 24 and gas 26 there is less resistance encountered by theimprint template 22 when it is brought into contact with the imprintliquid. This reduced resistance allows the imprint process to beundertaken more rapidly. Furthermore, the incidence of gas pocketsforming in the imprint pattern are reduced since the gas 26 is pushedaway from the center of the imprint template 22 due to the curvature ofthe imprint template 22.

Once the bent imprint template 22 has been brought into contact with theimprint liquid 24, the force applied by the actuator(s) 23 may bereduced, and the imprint template 22 thus flattened onto the imprintliquid 24 to imprint a pattern into the imprint liquid 24.

FIG. 4 shows a possible failing in a magnification correction technique.In FIG. 4, thermal expansion of an imprint template 41 has occurred, andthe force to offset this expansion has been calculated, as describedabove. However, in this case a gap 42 (shown exaggerated for thepurposes of the present drawing) is located between actuator(s) 43 andthe peripheral edge(s) of the template 41. As a result, not all of theforce generated on expansion of the actuator(s) 43 is applied to theimprint template 41, and instead, some expansion of the actuator(s) islost in expansion through the gap 42 before contact with the template'speripheral edge(s). The force applied to the template 41 is thuslessened, and the extent to which the template is deformed is reduced sothat features 41 a on the template do not align with features 44 a onthe substrate 44. It can be seen that the force applied to the templatein this case is improperly regulated.

It will be appreciated that a similar difficulty in regulation of theforce applied to a template may arise in the event that a supportstructure supporting the template and actuator(s) deforms under theurging of the actuator(s). In that case as well or alternatively, aportion of the force that would otherwise be applied by the actuator(s)to the imprint template is lost, and deformation of the imprint templateis less than would be expected. As a result desired deformation of theimprint template may not be achieved, and proper magnificationcorrection may not occur.

FIGS. 5a and 5b illustrate an imprint apparatus according to anembodiment of the present invention. FIG. 5a shows an underside view ofthe apparatus, and FIG. 5b illustrates a part section view of theapparatus of FIG. 5a taken along the line I-I.

The apparatus is shown as including an imprint template 50, which issubstantially planar in shape. The imprint template 50 has twosubstantially square surfaces, one of which is provided with a patternedregion 50 a. The imprint template 50 has four peripheral sides whichextend around the imprint template 50. Extending around the periphery ofthe imprint template 50 is a support structure 51. The support structure51 is connected to the imprint template 50 through piezoelectricactuators 52 and piezoelectric force sensors 53. The piezoelectricactuators 52 and piezoelectric force sensors 53 are connected in series,so that the piezoelectric actuators 52 abut the peripheral faces of theimprint template 50 and the piezoelectric force sensors 53, and thepiezoelectric force sensors 53 abut the piezoelectric actuators 52 andan interior face of the support structure 51. In the embodiment shownthe piezoelectric actuators 52 and piezoelectric force sensors 53project from the support structure 51, but in an embodiment theactuators 52 and sensors 53 may be accommodated in recesses in theimprint template 50 or support structure 51. When loaded in purebending, the neutral plane NP of the imprint template 50 is a planewhere compression and tension stresses are zero. The neutral plane NPextends through and across the imprint template and substantiallybisects each of the imprint template's 50 peripheral faces. As can beseen from FIG. 5b , the piezoelectric actuators 52 meet the imprinttemplate 50 at a location substantially on the template's neutral planeNP, and are thereby able to apply a force to the template that issubstantially on the neutral plane, and thus substantially even aboutthe neutral plane. While multiple actuators and force sensors aredepicted, a single actuator and force sensor, a single actuator and aplurality of force sensors, or a plurality of actuators and a singleforce sensor may be provided.

FIG. 6 shows in schematic form a possible mode of operation of theimprint lithographic apparatus according to an embodiment of theinvention. In FIG. 6a , a voltage is established across thepiezoelectric actuators 62 prior to imprinting, causing the actuators toexpand. The piezoelectric actuators 62 are thus urged against theperipheral edges of the imprint template 60, and against thepiezoelectric force sensors 63, compressing both the template 60 and thesensor 63. This compression of the piezoelectric force sensor 63 causesan electrical signal to be generated, this signal being indicative ofthe magnitude of the force applied to the sensor 63. The force beingapplied to the imprint template 60 is then compared with the amount offorce that has been calculated as necessary to provide appropriatemagnification correction. In the event that the force applied issufficient to provide the necessary correction then the correspondingvoltage is used for imprinting.

FIGS. 6b and 6c illustrate operation of an imprint lithographicapparatus of an embodiment of the invention when a gap 64 has arisenbetween one or more of the actuators 62 and the imprint template 60. Itwill be recognized that the presence of a gap anywhere in the path alongwhich a piezoelectric actuator 62 may apply force to a peripheral edgeof the imprint template 60 (for example, a gap between the piezoelectricactuators 62 and the peripheral edges as shown in FIG. 6b ) will reducethe amount of force applied to the piezoelectric force sensor 63 onexpansion of the piezoelectric actuator 62, and thus reduce the signalproduced by the sensor 63. This signal indicative of the reduced forceapplied to the piezoelectric force sensor is compared with the amount offorce that has been calculated to provide magnification correction. Inthe event that insufficient force is detected by the piezoelectric forcesensor 63 imprinting will not occur.

As shown in FIG. 6c , appropriate compensation for this reduction inforce may then be achieved by increasing the voltage applied to thepiezoelectric actuators 62, thus increasing their expansion tocompensate for the presence of the gap 64. The signal produced by thepiezoelectric force sensors 63 in response to this increased expansionof the piezoelectric actuators 62 may then be assessed once again. Ifthe force applied to the piezoelectric force sensors 63 remains too low,and thus the force applied to the imprint template 60 will still be toolow to provide magnification correction, a still larger voltage may beapplied across the piezoelectric actuators 62 and the force generatedassessed again. The process of increasing the voltage applied across thepiezoelectric actuators 62 and assessing the signal produced by thepiezoelectric force sensors 63 may then be repeated as often asnecessary until the signal representative of the force applied to thepiezoelectric force sensors 63, and thus to the imprint template 60,indicates that this force is sufficient to provide effectivemagnification correction. Once the voltage causing this required forceis established, this voltage may be applied to the piezoelectricactuators 62, the imprint template 60 deformed sufficient to correct formagnification, and imprinting can then take place.

In the case that the imprint lithography apparatus of an embodiment ofthe invention is to be used in magnification correction or shapecorrection, the force applied to the imprint template should be appliedsubstantially on the neutral plane of the template. This may be achievedby the provision of actuators 52 meeting the imprint template 50substantially at the neutral plane, as shown in FIG. 5b . Alternativelyor additionally, provision of force substantially in the neutral planemay be achieved by providing one or more actuators that meet the imprinttemplate on both sides of the neutral plane. An arrangement of animprint lithography apparatus in accordance with this embodiment of theinvention is shown in FIG. 7a . In FIG. 7a , it can be seen that thereare two layers of piezoelectric actuators 72 and force sensors 73attaching the imprint template 70 to the support structure 71. A firstlayer of piezoelectric actuators 72 a and piezoelectric sensors 73 a arelocated above the neutral plane NP of the imprint template 70. A secondlayer of piezoelectric actuators 72 b and piezoelectric force sensors 73b are located below the neutral plane NP of the imprint template 70. Thefirst and second layers of piezoelectric actuators 72 and force sensors73 extend substantially parallel to one another, and along the or eachrespective side of the support structure 71. In FIG. 7b thepiezoelectric actuators 72 a and 72 b are shown to provide a force tothe imprint template 70 that is substantially equal across both sides ofthe template's neutral plane NP. Once the piezoelectric force sensors 73a and 73 b determine that the force applied to the imprint template 70by the piezoelectric actuators 72 a and 72 b is sufficient to bringabout magnification correction, imprinting may occur. While multipleactuators and force sensors are depicted, a single actuator and forcesensor, a single actuator and a plurality of force sensors, or aplurality of actuators and a single force sensor may be provided.

The use of actuators that meet the imprint template at a positiondisplaced from the neutral plane allows an imprint lithography apparatusin accordance with an embodiment of the present invention to be used inimprint lithography using a bent template, as described above inrelation to FIG. 3. Such an arrangement is shown in FIG. 7c . If a forcedirected towards the center of the imprint template 70 is applied to theperipheral face(s) of the imprint template 70 unevenly above or belowthe neutral plane, the imprint template 70 can be made to bend up ordown (in relation to the orientation of the imprint template 30 shown inFIG. 7c ) depending on whether the greater force is applied above orbelow the neutral plane NP. It will be appreciated that this effect maybe achieved by the application of a force on only one side (i.e. aboveor below) the neutral plane NP. Alternatively this may be achieved byapplication of force on both sides of the neutral plane NP, as long as arelatively greater force is provided one side of the neutral plane thanthe other.

It will be appreciated that an imprint lithography apparatus of anembodiment of the invention incorporating layers of piezoelectricactuators and piezoelectric force sensors may be used to regulate theforce applied to an imprint template, and thus control the degree ofcurvature attained.

As shown in FIG. 7a , when no voltage is applied to the piezoelectricactuators 72 a, 72 b, these do not expand and thus do not apply anyforce to the imprint template 70, or to the piezoelectric force sensors73 a, 73 b positioned between the actuators and the support structure71.

When a voltage is applied across the first layer of piezoelectricactuators 72 a these actuators undergo a converse piezoelectric effect,and deform such that they apply a force towards the center of thetemplate 70 and through the piezoelectric sensors 73 a towards thesupport structure 71. Since the force applied to the template 70 isapplied above the neutral plane NP it causes the imprint template 70 tobend downwards. The force applied by the piezoelectric actuators 72 athrough the piezoelectric force sensors 73 a causes these sensors toundergo a direct piezoelectric effect, in which force applied to thesensors 73 a causes the generation of an electrical potential. Themagnitude of this potential is indicative of the force applied to thepiezoelectric force sensors 73 a, and so may be used to assess theeffective force applied by the piezoelectric actuators 72 a to thetemplate 70. This force may then be compared with a force known to berequired to impart a desired level of curvature to the imprint template70. In the event that the force applied to the imprint template 70 isless than the required force, then the voltage applied across thepiezoelectric actuators 72 applying the force may be increased. In theevent that the force applied to the imprint template 70 is greater thanthe force required to impart the desired curvature, then the voltageapplied across the piezoelectric actuators 72 may be decreased.

When the imprint template 70 and patterned region 70 a have been made tobend downwards, the imprint template 70 can be used in the same way asdescribed in relation to the bent template 22 of FIGS. 2a and 2b . Oncethe bent imprint template 70 comes into contact with imprint liquiddeposited on a substrate, the difference between the forces appliedabove and below the neutral plane are reduced, causing the imprinttemplate 70 to flatten. This reduction in the differential between thetwo forces may be achieved by reducing the previously greater force (sothat it more closely approximates the previously lower force) and/or byincreasing the previously lower force (so that it more closelyapproximates the previously higher force). By way of example, in thecase that it is wished to reduce the previously greater force, thevoltage applied across the upper layer of piezoelectric actuators 72 amay be reduced. In the case that it is wished to increase the previouslylesser force, the voltage applied across the lower layer ofpiezoelectric actuators 72 b may be increased. In the event that it iswished to undertake a magnification or shape correction associated withthe imprinting, a suitable voltage may be applied substantially equallyacross both layers of piezoelectric actuators 72 a and 72 b, resultingin both flattening of the imprint template and its deformation suitableto put into effect a correction process.

FIG. 8 shows a detail of an imprint lithography apparatus in accordancewith an embodiment of the present invention. An imprint template 80 isconnected to a support structure 81 by means of piezoelectric actuators82 and piezoelectric force sensors 83. The piezoelectric actuators 82and piezoelectric force sensors 83 are arranged in series, and elastichinges 84 are provided on each side of the paired actuators and forcesensors. These elastic hinges 84 help to protect the piezoelectricactuators 82 and piezoelectric force sensors 83 against bending momentsthat may otherwise damage the piezoelectric elements.

An imprint lithography apparatus in accordance with an embodiment of theinvention may be provided with a plurality of actuators and/or with aplurality of force sensors. The most suitable number of actuators and/orforce sensors may be determined with reference to the size of theimprint template, and with reference to the effect that is to beachieved (e.g. magnification correction, and/or shape correction, and/oruse of the imprint template as a curved template). The number, type andarrangement of actuators and/or sensors may vary depending on thestructure of the imprint template itself. For example, for an imprinttemplate having an area of 30 mm² with a 25 mm² patterned region, whenactuators and force sensors are paired in series, a particularlysuitable arrangement is to provide seven such pairs per side of theimprint template. However, any suitable number of actuators and/or forcesensors may be used.

For the purposes of the present disclosure the imprint template shouldbe taken to comprise any structure used to transfer a pattern onto asubstrate, and that is able to be deformed under the urging of anactuator, for example to allow a magnification correction or sizecorrection technique to be practiced. It will be appreciated that thetemplate will comprise both those features that contact that substrate,and any structure on which such features are carried (which may bemanufactured as a whole with these features, or, for example, as aseparate holder). Suitable deformation may be achieved by theapplication of force to the features directly, or to any structure onwhich these features are carried.

An imprint lithography apparatus according to an embodiment of theinvention has been described with reference to the use of piezoelectricactuators and piezoelectric force sensors. For the purposes of thepresent disclosure, references to piezoelectric force sensors should betaken to encompass piezoresistive force sensors (in which theapplication of pressure induces a change in the electrical resistance ofmaterial of the force sensor). Indeed, piezoresistive force sensorsrepresent a desired force sensor for use in an apparatus or method of anembodiment of the invention.

It will be appreciated that one or both of the actuators or forcesensors may be replaced with an alternative actuator and/or force sensorsuch as a hydraulic miniature piston, or a compact linear electricalmotor and lever (the lever being used to magnify the force generated bythe linear motor to generate force of sufficient magnitude to deform theimprint template). Any suitable actuator configured to impart a force onthe imprint template may be used, as may any suitable force sensorconfigured to sense a force applied to the template.

In certain circumstances (e.g. where reduced temperature has causedcontraction of an imprint template, or in a certain shape correctionapplication), it may be desirable to utilize actuators configured toinduce the template to expand by placing the template under tension(i.e. by pulling on the template). In such a case, a suitable forcesensor would one configured to sense the force applied in causing suchexpansion.

The embodiments thus far have been shown with an actuator and forcesensor arranged in series, however an embodiment may, alternatively oradditionally, make use of an actuator and force sensor arranged inparallel.

In an apparatus in which the actuators and force sensors are arranged inseries, the order of these components may be substituted withoutdetracting from one or more of the advantages described herein. Anembodiment has been described with reference to an apparatus in whichthe actuators abut the imprint template, and in which the force sensorsabut the support structure. In embodiment, this order of actuator andforce sensor may be reversed. Indeed, in any embodiment describedherein, neither the actuator nor the force sensor need directly abut theimprint template, as long as they are configured such that the actuatoris able to apply a force to the imprint template, and the force sensoris able to sense the force applied to the template to allow anassessment of this force to be made. In light of the above, it will beappreciated that a suitable force sensor may be any sensor able toprovide an indication of the force applied to the template.

The preceding descriptions have related to embodiments in which theforce applied to the imprint template is assessed by means of sensorsthat are compressed on application of such a force. However, the forceapplied to the imprint template may be assessed by extension of forcesensors located between the support structure and the imprint template.This arrangement may be of use in an apparatus in which the forceactuators and sensors are arranged in parallel. In this case,compression of the imprint template by the actuators will result in anextension of force sensors positioned in parallel with the actuators,and this extension may be used to determine the amount of compressionoccurring through the action of the actuators. In this case the forcesensor may comprise an elongation sensor which may be used to report onthe amount of force applied to the imprint template. This may, forexample, be achieved by use of a reference value, in which a givenextension of the sensor is known to correlate with a given amount offorce applied to the imprint template. In the event that the forceactuators and force sensors are arranged in parallel, it may bedesirable that the force sensor be used to sense force applied to theimprint template by an actuator adjacent the force sensor.

The embodiments of the invention described thus far have been providedwith both actuators and force sensors on all sides of the imprinttemplate. An embodiment may provide actuators and/or force sensors onthree sides of a four-sided imprint template, on two sides of an imprinttemplate (e.g., on non-opposing sides), or even on one side of animprint template. In an apparatus in which the actuators and forcesensors are arranged in series, these components may be provided ondifferent sides of the imprint template (e.g. an arrangement withactuators only on one side of the imprint template, and force sensorsonly on an opposing side of the imprint template), as long as the forcesensors are arranged such that they can assess the force applied to theimprint template.

When a voltage is applied across a piezoelectric actuator, the forceimparted to the force sensor, and hence to the template, is compared tothat which has been calculated to be desired (e.g. for magnification orshape correction, or to cause curvature of the template), and imprintingoccurs once the voltage producing the requisite force has beenestablished. If the force is too low, the voltage applied to thepiezoelectric actuator is increased, and the force applied assessed andcompared once more. If the force is too great, the voltage applied tothe piezoelectric actuator is decreased, and the force applied assessedand compared once more. It will be appreciated that the increase ordecrease of the voltage may take place in a “step” fashion (i.e. througha series of discrete increases or decreases, which may be separated byperiods at which substantially no voltage is applied across thepiezoelectric actuators, each followed by an assessment of force), ormay take place in a “ramped” fashion, in which the voltage is changedrelatively steadily until the requisite force is achieved (withassessment of the force conducted either continuously or at suitableintervals). It may be desirable that a voltage be maintained across anactuator at the same time that the force imparted as a result of thevoltage is assessed.

The force that may be applied to an imprint template in order to causesuitable magnification or shape correction, or to impart a desireddegree of curvature, may be readily determined by those skilled in theart. By way of example, a suitable method by which such a determinationmay be made includes the use of a linear elasticity model. In the caseof a magnification correction, it may be desirable to calculate thedesired force analytically. When the template may require a complexshape correction, it may be desirable to use a finite element method orfinite volume method. A suitable method may use a simplified model inwhich some desired values are interpolated between calculated values.

It will be appreciated that, in the case of actuators and force sensorsutilizing electrical power or signals, suitable electrical connectionsshould be provided as part of the apparatus. Suitable connections may beshielded connections.

The preceding description has considered an imprint template andsubstrate that are of substantially square shape. An apparatus andmethod of an embodiment of the invention may, alternatively oradditionally, be used with a substrate and/or template having adifferent shape. Merely by way of example, this may include arectangular template or substrate, or trapezoidal substrate or template.The in-plane shape or magnification correction techniques that may beput into practice using an apparatus or method of an embodiment of theinvention are also able to counteract unidirectional elongation andpin-cushion effects.

For illustrative purposes, the gaps referred to in the precedingparagraphs (and shown in the accompanying drawings) have been shown asvoids in which no material is present. However, it would be appreciatedthat gaps may be filled with relatively soft material, such as glue orthe like. Indeed, for the purposes of present disclosure, a gap shouldbe taken as comprising any region where there is an absence of amaterial having sufficient stiffness to allow the urging of an actuatoracting against the material to be transferred to an imprint template.Thus a gap may comprise a void, or may comprise an area of relativelysoft material (effectively a gap for the present purposes).

In an embodiment, there is provided the following according to thefollowing clauses:

1. An imprint lithography apparatus comprising: a support structureconfigured to hold an imprint template; an actuator located between thesupport structure and a side of the imprint template, when the imprinttemplate is held by the support structure, configured to apply a forceto the imprint template; and a force sensor between the supportstructure and a side of the imprint template, when the imprint templateis held by the support structure.

2. The imprint lithography apparatus of clause 1, wherein the forcesensor is configured to measure a pressure applied to the imprinttemplate.

3. The imprint lithography apparatus of clause 1, wherein the forcesensor comprises a plurality of force sensors.

4. The imprint lithography apparatus of clause 1, wherein the forcesensor comprises a piezoelectric sensor.

5. The imprint lithography apparatus of clause 4, wherein thepiezoelectric sensor comprises a piezoresistive force sensor.

6. The imprint lithography apparatus of clause 1, wherein the sensor isin series with the actuator.

7. The imprint lithography apparatus of clause 1, wherein the sensor isin parallel with the actuator.

8. The imprint lithography apparatus of clause 1, further comprising ahinge, the hinge in series with the actuator.

9. The imprint lithography apparatus of clause 8, wherein the hingecomprises an elastic hinge.

10. The imprint lithography apparatus of clause 1, wherein the actuatoris configured to meet the imprint template at a location substantiallyon the neutral plane of the imprint template.

11. The imprint lithography apparatus of clause 1, wherein the actuatoris configured to meet the imprint template at a point removed from theneutral plane.

12. The imprint lithography apparatus of clause 1, wherein the actuatorcomprises a plurality of actuators.

13. The imprint lithography apparatus of clause 1, wherein an actuatoris located on each side of the neutral plane of the imprint template.

14. The imprint lithography apparatus of clause 1, wherein the actuatorcomprises a piezoelectric actuator.

15. The imprint lithography apparatus of clause 1, comprising anactuator selected from the group consisting of a hydraulic piston and anelectric motor.

16. An imprint lithography apparatus, comprising: an imprint templatesupported by a support structure; an actuator, located between thesupport structure and a side of the imprint template, configured toapply a force to the imprint template; and a force sensor locatedbetween the support structure and a side of the imprint template.

17. An imprint lithography method, comprising: applying a force to aside of an imprint template; assessing the force applied to the imprinttemplate by means of a force sensor; and determining whether the forceapplied to the imprint template is sufficient to achieve a desireddeformation of the imprint template.

18. The imprint lithography method of clause 17, wherein the desireddeformation of the imprint template is a compression of the imprinttemplate sufficient to allow magnification correction of the imprinttemplate.

19. The imprint lithography method of clause 17, wherein the desireddeformation of the imprint template is a compression of the imprinttemplate sufficient to allow shape correction of the imprint template.

20. The imprint lithography method of clause 17, wherein the desireddeformation of the imprint template is an extension of the imprinttemplate sufficient to allow magnification correction of the imprinttemplate.

21. The imprint lithography method of clause 17, wherein the forceapplied to the imprint template is increased or decreased through aseries of discrete increases or decreases until a desired deformation ofthe imprint template is achieved.

22. The imprint lithography method of clause 17, wherein the forceapplied to the imprint template is increased or decreased steadily untila desired deformation of the imprint template is achieved.

23. An imprint lithography method, comprising: applying a force to aside of an imprint template; assessing the force applied to the imprinttemplate by means of a force sensor; and determining whether the forceapplied to the imprint template is sufficient to achieve a desiredcurvature of the imprint template.

24. The imprint lithography method of clause 23, wherein the forceapplied to the imprint template is increased or decreased through aseries of discrete increases or decreases until a desired curvature ofthe imprint template is achieved.

25. The imprint lithography method of clause 23, wherein the forceapplied to the imprint template is increased or decreased steadily untila desired curvature of the imprint template is achieved.

26. The imprint lithography method of clause 23, wherein the force isapplied to the imprint template by a piezoelectric actuator.

27. The imprint lithography method of clause 23, wherein the forceapplied to the imprint template is assessed by a piezoelectric forcesensor.

28. An imprint lithography apparatus comprising an imprint templatesupported by a support structure, an actuator located between thesupport structure and a side of the imprint template configured to applya force to the imprint template, wherein the actuator is arranged toapply a force to a side of the imprint template at a positionsubstantially on the neutral plane of the imprint template.

29. An imprint lithography apparatus comprising a support structureconfigured to support an imprint template, the support structurecomprising an actuator arranged to apply a force to a side of theimprint template at a position substantially on the neutral plane of theimprint template.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the present invention as described without departing fromthe scope of the claims set out below.

What is claimed is:
 1. An imprint lithography method, comprising:applying a force to a side of an imprint template; assessing the forceapplied to the imprint template by means of a force sensor; anddetermining whether the force applied to the imprint template issufficient to achieve a desired curvature of the imprint template. 2.The imprint lithography method of claim 1, wherein the force applied tothe imprint template is increased or decreased through a series ofdiscrete increases or decreases until a desired curvature of the imprinttemplate is achieved.
 3. The imprint lithography method of claim 1,wherein the force applied to the imprint template is increased ordecreased steadily until a desired curvature of the imprint template isachieved.
 4. The imprint lithography method of claim 1, wherein theforce is applied to the imprint template by a piezoelectric actuator. 5.The imprint lithography method of claim 1, wherein the force applied tothe imprint template is assessed by a piezoelectric force sensor.
 6. Theimprint lithography method of claim 1, wherein applying the force to theside of the imprint template comprises applying the force to the imprinttemplate but not at a point of contact on a neutral plane of the imprinttemplate.
 7. The imprint lithography method of claim 1, wherein anactuator to apply the force is located between a support structure tosupport the imprint template and the side of the imprint template, theforce sensor is between the support structure and the side of theimprint template and in direct contact with the support structure, andthe force sensor is in parallel with the actuator.
 8. The imprintlithography method of claim 7, wherein the force sensor comprises apiezoelectric sensor.
 9. The imprint lithography method of claim 1,wherein the desired curvature of the imprint template is a result of acompression or extension of the imprint template sufficient to allowmagnification correction of the imprint template.
 10. The imprintlithography method of claim 1, wherein the desired curvature of theimprint template is a result of a compression of the imprint templatesufficient to allow shape correction of the imprint template.
 11. Theimprint lithography method of claim 1, wherein assessing the forceapplied to the imprint template comprises measuring a pressure appliedto the imprint template.
 12. An imprint lithography apparatuscomprising: a support structure configured to hold an imprint template;an actuator configured to apply a force to a side of the imprinttemplate; a sensor configured to assess the force applied to the imprinttemplate; and a control system configured to determine whether the forceapplied to the imprint template is sufficient to achieve a desiredcurvature of the imprint template.
 13. The imprint lithography apparatusof claim 12, wherein the control system is configured to cause the forceapplied to the imprint template to be increased or decreased through aseries of discrete increases or decreases until a desired curvature ofthe imprint template is achieved.
 14. The imprint lithography apparatusof claim 12, wherein the control system is configured to cause the forceapplied to the imprint template to be increased or decreased steadilyuntil a desired curvature of the imprint template is achieved.
 15. Theimprint lithography apparatus of claim 12, wherein the support structureand the actuator are arranged such, when the imprint template issupported by the support structure, that the force is applied to theimprint template but not at a point of contact on a neutral plane of theimprint template.
 16. The imprint lithography apparatus of claim 12,wherein the sensor comprises a piezoelectric sensor.
 17. The imprintlithography apparatus of claim 12, wherein the actuator is locatedbetween the support structure and the side of the imprint template whensupported on the support structure, the sensor is between the supportstructure and the side of the imprint template when supported on thesupport structure and in direct contact with the support structure, andthe sensor is in parallel with the actuator.
 18. The imprint lithographyapparatus of claim 12, wherein the sensor is configured to measure apressure applied to the imprint template.
 19. The imprint lithographyapparatus of claim 12, wherein the actuator comprises a piezoelectricactuator.
 20. The imprint lithography apparatus of claim 12, wherein thedesired curvature of the imprint template is a result of a compressionor extension of the imprint template sufficient to allow magnificationcorrection of the imprint template.